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Topic: Subscript on plus expression
Replies: 16   Last Post: Dec 3, 2012 3:18 AM

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 Dave Snead Posts: 52 Registered: 12/13/04
Re: Subscript on plus expression
Posted: Nov 19, 2012 5:05 PM

Nasser --,

I'm using these as tensor indices.

Although Bob Hanlon offered a workaround (thanks Bob)
Format[Subscript[arg_Plus, k_]] :=
Subscript["(" <> StringJoin @@
Riffle[ToString /@ (List @@ arg),
" + "] <> ")", k]
Subscript[a + b + 2, k],

I think the folks at Mathematica should fix this and insert the parentheses.
The output of Subscript[Plus[a,b],k] should not be represented as
Plus[a,Subscript[b,k]]!

-- Dave

-----Original Message-----
From: Nasser M. Abbasi
Sent: Sunday, November 18, 2012 2:13 PM
Subject: Re: Subscript on plus expression

On 11/18/2012 3:03 AM, Dave Snead wrote:
> Hi,
>
> Mathematica fails to parenthesize the a+b in
> Subscript[Plus[a,b],k]
>
> so the output looks identical to
> Plus[a,Subscript[b,k]]
>
> Is this a bug?
> Is there an option to force the parentheses?
>
>
>
>

Actually, just typing

(a+b)
k

and then hitting ENTER will result in

a+b
k

i.e. the () are gone. Same effect you showed.

It might be because subscript are meant to be applied to an atomic symbol
and not combined expression like a+b. I do not know. I am not even sure
what (a+b)_k is supposed to mean, math wise. Is this meant to
be on the code or in a text cell? If it is in the code itself,
how will it be used?

--Nasser

Date Subject Author
11/18/12 Nasser Abbasi